Granular detergents have so far been principally prepared by spray drying. In the spray drying process the detergent components, such as surfactants and builders, are mixed with as much as 35-50% water to form a slurry. The slurry obtained is heated and spray dried which requires high energy input and expensive equipment. An efficient method of processing detergents without slurrying in water and then subsequently drying would be less expensive.
Processes for "dry" neutralization (ie essentially water free) are well-known and practiced by detergent manufacturers in the manufacture of detergent granules of high bulk density, in particular for the neutralization of acid forms of anionic surfactants.
There is a need however to produce agglomerates that have cleaning performance comparable with conventional spray-dried granules.
It has been discovered that the rate and the completeness of the neutralization reaction can have an impact on the performance and rate of solubility of the detergent granules and therefore represent an important consideration for the commercial application of such a process.
It has now been surprisingly found that the use of finely ground particulate neutralizing agent of a narrowly defined particle size optimises the said neutralization reaction, and in so doing, realises benefits in the performance and rate of solubility of detergent granules of high bulk density made by such "dry" neutralization processes. The detergent granules made by the invention have a bulk density greater than 650 g/l.
U.S. Pat. No. 4,515,707, published May 7, 1985, describes a process for dry neutralization of a detergent sulphuric or sulphonic acid with sodium carbonate powder in the presence of powdered sodium tripolyphosphate in a high shear mixer. The resulting powder is used in the manufacture of solid detergent bars.
Japanese Pat. No. 60 072 999 discloses a batch process whereby a detergent sulphonic acid, sodium carbonate, water and other optional ingredients are brought together in a high shear mixer followed by cooling to 40.degree. C. or below and pulverising with zeolite powder and granulating.
EP A 0 420 317, published Apr. 3, 1991, discloses a continuous process whereby a detergent sulphonic acid, particulate inorganic material, water and other optional ingredients are brought together in a high speed mixer/densifier. Material is subsequently treated in a moderate speed granulator/densifier. Addition of fine powders in the second step, or between the first and second step, is described as beneficial for the agglomeration process.
EP A 0 430 603, published Jun. 5, 1991, discloses a process for preparing high active detergent agglomerates using a finely divided particulate filler with a high oil absorption value as a processing aid for the agglomeration step.